A number of medical diagnostic imaging systems known in the art are examples of systems which would be improved by implementing the basic concept of the present invention.
In general, the prior art systems utilize detectors to sense radiation such as X or .gamma. flux interacting with the detectors and to convert each quantum of X- or .gamma.-rays to individual electrical output pulses or to convert integrated inputs to proportional electrical outputs. Location-computing circuitry calculates the X and Y coordinates of each interaction and thus identifies the elemental area of the detector or array of detectors within which an interaction (event) occurs to a given accuracy. The systems further process and display images produced from the detected data. For example, the present invention may be implemented as a data processing means for a Gamma Camera (Scintillation Camera) of the Anger type. Such cameras are widely used in Nuclear Medicine as radiation detectors for determining the distribution of a radioactive substance in a body. The camera converts images formed by gamma radiation into a related visible image. See, for example, U.S. Pat. No. 3,011,057 in which typical Gamma Camera apparatus is disclosed for collecting information from patients after the administration of radio-nuclides through inhalation, ingestion or injection.
The present invention can also be used in Computerized Axial Tomography (CAT) and ultrasound imaging, as well as in non-diagnostic systems such as starlight intensifiers, radar systems and so on. Apparatus for performing Computerized Axial Tomography, for example, produces a representation of the absorption coefficients of penetrating radiation from a source of X-rays at a plurality of elemental locations distributed over a cross-sectional slice of a body under investigation. Such apparatus well-known to the persons skilled in the art is disclosed, for instance, in the instance, in the U.S. Pat. No. 3,778,614.
Regardless of the nature of the body being examined, and the type of radiation, only those beams incident on a radiation detector in accordance with the present invention contribute to the outputs of the detector.
As used herein the "actual physical data" that is being measured, processed and used, means either a distribution (spatial or projected) of absorption density, such as tissue density in the case of X-rays, a distribution of radioisotope concentration in the case of .gamma.-rays, a distribution of tissue interfaces in the case of ultrasound detection, or a distribution of radar reflectors, optical sources or reflectors and so on, depending on the case.
The actual physical data obtained from Gamma Camera or CAT systems includes significant amounts of "statistical noise".
The "statistical noise" is the random variation between the "true" value, which would have been achieved by imaging the object with infinite radiation and the actual measured values which also depend on the statistical variability of finite radioactive or absorption events. Conventional data processing techniques, for example those producing and displaying images obtained from Gamma Camera or CAT systems, include arrangements for reducing the statistical noise. More particularly, smoothing of different types, filters of different types and correctors of different types are provided, all of which are based on some "global" assumption such as the known aperture of the system or the known resolution limit below which everything is considered as "statistical noise". These "global" assumptions, as used in the prior art, have often tended to degrade the images by either actually increasing the noise or reducing the resolution, because of variations between the local case and the global assumptions. Thus, there is a long felt need for means other than prior art arrangements for reducing the statistical noise.